The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
To meet nitrogen oxide (NOx) emission requirements for a vehicle with a diesel engine, urea may be injected into an exhaust stream. The urea is stored in a tank that may be similar to a conventional fuel tank. Since the emissions impact of running out of urea is severe, correct urea level indication is required to inform the driver. For example, the vehicle may be required to operate in a limp home mode when the urea runs out.
Several unique characteristics of urea delivery systems make urea level sensing systems and on board diagnostic (OBD) monitoring different than fuel level monitoring systems. For example, urea freezes at low temperatures. In addition, the volume of urea consumed per mile may be as low as 5 gallons for 4000 miles. Level sensing systems may be required to independently verify range readings from the sensor.